The invention relates to an electron accelerator comprising a target exposed to the electron beam for the purpose of producing x-ray bremsstrahlung, with a conical compensating member arranged in a centered fashion in the x-ray cone, as well with a collimator limiting (or defining) the x-ray cone.
The x-ray cone issuing from electron accelerators which are used in radiation therapy is to have a dose rate of equal magnitude over its entire cross-section. This is necessary in order to be able to apply the minimum dose required for destroying the diseased tissue in the region of the seat (or nidus) of the disease, and, at the same time, to be able to spare, insofar as possible, the adjacent healthy tissue.
In the case of electron accelerators wherein x-ray bremsstrahlung is produced in a so-called target through declaration of the electrons, the dose rate in the x-ray cone being issued has a conical characteristic with a maximum in the direction in which the electron beam impinges upon the target. This maximum most often coincides with the symmetry axis of the collimator. It is known to compensate the dose rate in the x-ray cone defined (or diaphrammed-out) by the collimator by installing a compensating member in the x-ray cone. Said compensating member has a conical construction. It is adapted in its form and in its radiation absorption properties to the characteristic of the dose rate at its point of application. In the case of electron accelerators provided with a compensating member in the aforementioned manner, an x-ray cone is issued whose dose rate is of equal magnitude at a fixed tissue depth (generally 10 cm) over the entire cross-section of the x-ray cone. At a lesser tissue depth, the dose rate, as illustrated in FIG. 2 with the drawn-out (or extended) solid line curve, increases from the interior toward the exterior. This can lead to a non-uniform dose distribution in the seat of the tumor or it can lead to a greater dose charge (or burden) on the healthy tissue.